The present invention relates to a process for producing coated synthetic bodies during which, before the coating, the surface to be coated is subjected to a pretreatment in an excited gas atmosphere.
The present invention is based on the understanding that, in producing coated synthetic bodies, the synthetic material, the coating material as well as the coating process determine the additional specific measures for obtaining a satisfactory coating adhesion on the synthetic surface. This results in an extremely large variety of different additional measures which must be taken in order to ensure, in each case, specifically, the adhesion of a certain coating on a synthetic body of a certain material.
Therefore, the following explanations only have the purpose of showing examples and corresponding known starting points of solutions.
From the lecture by G. Legeay, xe2x80x9cSurface Modification of Natural or Synthetic Polymers by Cold Plasmasxe2x80x9d, given at the 2nd Conf. Plasma Chem. Tech. 1984, it has become known to increase the adhesion of a metal coating on synthetic surfaces by a prior plasma treatment of the surface. For example, oxygen-containing, helium-containing and carbon-containing gases are used for the plasma pretreatment.
The use of helium or oxygen plasma discharges for treating synthetic surfaces is also known from the technical essay by J. Hall from J. Appl. Polym. Sci. Vol. 13, 1969. The plasma treatment explained here has the object of achieving an improved conglutinating capacity of synthetic materials.
From the technical essay by J. Hollahan from J. Appl. Polym. Sci. Vol 13, 1969, it has been known to expose synthetic materials to a plasma treatment by ammonia-containing, nitrogen-containing and hydrogen-containing gas for improving the surface adhesion and the wettability. In such an application, a high-frequency plasma discharge is used. In U.S. Pat. No. 4,957,603, the difficulties are discussed which occur when coating optical disks made of PMMA, namely that this synthetic material is particularly difficult to coat when a cathode atomization process is used. Another known process for increasing the adhesion of a coating on synthetic surfaces is the intermediate coating by oxides or nitrides.
For metal coating particularly a PMMA synthetic body by magnetron cathode atomizing, EP 0 507 113 suggests that the coating be carried out in a plasma-excited gas atmosphere of argon and at least another inert gas, and in the process change the mixture ratio of the gas atmosphere in a controlled manner during the coating process.
DE 197 52 889 suggests improvement of the abrasion resistance of applied indium tin oxide (ITO) layers on optical components, such as monitoring windows, flat panel displays, cathode ray tubes, in that, during the coating operation, the surface to be coated is bombarded with argon ions with an energy of from 60 eV to 90 eV. When coating organic surfaces, for example, polymethylmethacrylate (PMMA), before the coating, a plasma treatment is carried out on the surface in a vacuum while feeding reactive oxygen and gas containing water.
CH 688 042, it is known to provide a synthetic surface by a magnetic-field-supported atomizing in a gas atmosphere of argon-containing and carbon-containing gas.
Furthermore, during the sputter coating of PMMA surfaces, in contrast to the coating of polycarbonate surfaces, during the target change, that is, when a new target is used, or during a longer opening of the process chamber with respect to the ambient atmosphere, problems occur because of the fact that the sputtering surface of the target is covered by an oxide layer. For the sputtering-away of this oxide layer, a better vacuum is required in the starting phase than when the coating process is in progress. The strong gas exhalation of the PMMA, in comparison, for example, to polycarbonate, impairs the vacuum conditions such that a change from the so-called oxide mode to the metallic mode is made impossible. This problem can be solved in that, for the presputtering, that is, for starting the process, argon is used as the sputtering gas and polycarbonate disks are used as dummy substrates. This considerably complicates and prolongs the starting procedure. The fact that aluminum coatings adhere poorly to polycarbonate surfaces, is intentionally utilized by Warner Advanced Media Operation, specifically for producing DVD14 and DVD18 disks.
An object of the present invention is to provide a process which
(a) in practice, is to be usable as a standard process, within wide limits independently of the material of the synthetic surface to be coated, of the used coating technique and of the used coating material. It has the purpose of ensuring an equally good adhesion of the applied coating particularly for materials which, as known, are difficult to coat, such as especially PMMA, but also for less critical synthetic materials, such as polycarbonate, bismaleimide triazine (BT) resins, fire-inhibiting epoxy glass laminates, particularly FR4 as well as for surfaces which are to be coated with photosensitive resists and/or solderable lacquers as well as similar materials of the semiconductor industry and for printed circuit board materials, and
(b) solves the above-mentioned problems when sputter coating PMMA and similar materials.
According to the invention, this object is achieved by predominantly forming the gas atmosphere of argon, nitrogen and/or hydrogen, and limiting the ionic energy in the gas atmosphere and in the area of the surface to be coated to not more than 50 eV. In this case, the ionic energy is preferably selected to be not more than 20 eV, preferably not more than 10 eV.
Surprisingly, as a result of the combination of the above-mentioned gas atmosphere and of the above-mentioned low ionic energies, the above-mentioned objects are combinantly achieved. If, for example, oxygen is used instead of hydrogen and/or nitrogen, this effect cannot be achieved, no matter whether or not the condition with respect to the ionic energy has been met. This effect also does not occur in the case of a hydrogen plasma and/or nitrogen plasma, at which higher ionic temperatures occur, as normally takes place in the case of a plasma excitation at HF.
Thus, according to the invention, a low-energy argon/nitrogen and/or hydrogen plasma is used for the pretreatment of the synthetic surfaces to be coated.
In this case, the excitation of the gas atmosphere preferably takes place by way of a plasma discharge or by UV radiation. Low-energy plasmas which are primarily suitable for the use within the scope of the present invention are microwave or ECR discharges, but preferably low-voltages discharges. HF or timed DC plasma discharges can be used if the pressure conditions are selected correspondingly and/or the discharge is maintained so far away from the synthetic surface to be pretreated that the above-mentioned low-energy conditions are met on the above-mentioned surface. As mentioned above, a low-voltage discharge is preferably used; preferably with an electron-emitting hot cathode or the gas excitation by means of UV radiation with H and N lines.
Argon is preferably used as the noble gas.
Surprisingly, it was found during the implementation of the production process according to the invention that significant advantages are obtained other than with respect to the adhesion of the subsequently applied coating and with respect to the implementation of the process when sputter coating PMMA surfaces or surfaces of similar critical synthetic materials as a result of the above-mentioned pretreatment according to the invention, the production process can also easily be carried out while including a storage time of the pretreated synthetic surfaces in a normal atmosphere. That is, the surfaces pretreated within the scope of the process according to the invention are passivated, this passivation, for being undone, subsequently requiring no further measures for the further treatment, specifically for the coating.
In a preferred embodiment of the process according to the invention, the coating is carried out by a vacuum coating process. In this case, plasma polymerization, a reactive or non-reactive PVD process or a PECVD process is preferably used.
In a particularly preferred manner, the coating takes place by plasma polymerization or by reactive or non-reactive sputtering; in this case, preferably by magnetron sputtering or by a reactive or non-reactive vapor coating; whether by electron beam vaporizing, by vaporizing from a heated crucible or by spark vaporizing.
Furthermore, the process according to the invention is used particularly on the above-mentioned critical synthetic materials, specifically on PMMA surfaces or surfaces consisting of BT or FR4.
Furthermore, the synthetic body is preferably coated with a metal or a metal compound, such as a nitride, oxide, carbide or their mixed forms.
The production process according to the invention is particularly preferably used for the production of optical disks, for the production of optical components, for printed circuit boards or for components in the field of semiconductor manufacturing.